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ATEL # 1228; S. Brandt, J. Chenevez, (DNSC, Denmark), E. Kuulkers (ESA/ESAC, Spain), L. Natalucci, M.T. Fiocchi, A. Tarana (INAF-IASF, Italy), S. Shaw (Southampton, UK), V. Beckmann, T. Courvoisier (ISDC, Switzerland), A. Domingo (LAEFF/INTA, Spain), K. Ebisawa (ISAS, Japan), P. Jonker (SRON, The Netherlands) P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), T. Oosterbroek (ESA/ESTEC, The Netherlands), A. Paizis (INAF-IASF, Italy), D. Risquez (LAEFF/INTA, Spain), C. Sanchez-Fernandez (ESA/ESAC, Spain), R. Wijnands (UvA, The Netherlands)
on 4 Oct 2007; 14:42 UT
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Subjects: X-ray, Neutron Stars, Transients
The recurrent transient neutron star system SAX J1747.0-2853 has in the past shown various outbursts with about 60 days duration.
Recent observations with INTEGRAL reveal that SAX J1747.0-2853 shows increased activity which may mark the beginning of a new outburst.
During the INTEGRAL Galactic Bulge monitoring observation (see ATels #438, #874 and #1004) from 2007 Oct 2 23:52 to Oct 3 03:34 (UT) the source had an intensity of 77+-3 mCrab in the 3-10 keV band and 19 +-3 mCrab in the 10-25 keV band of the JEM-X monitor. This is to be compared with 7 +-1 mCrab (2-10 keV) and 10 +- 1 mCrab (10-25 keV) observed on Sep 24-26 as part of the INTEGRAL key program. This shows the source to be brightening.
Two type-I X-ray bursts were detected by JEM-X on UT 2007 Sep 25 22:13:34 and on 2007 Sep 26 10:04:30, also confirming the active state of the source.
We further note that the timing of the peak of past outbursts by SAX J1747.0-2853 in 1998 (see Natalucci et al. ApJ 543, L73, 2000), RXTE/ASM (1996,2000,2001,2004,2006) and INTEGRAL (2004,2005,2006, see ATELS #256,#642,#734) are all consistent with an underlying periodicity of about 185 days.
Since the first outburst observed by the ASM in 1996 almost 21 periods has elapsed, with the source only showing major outbursts of about 60 days duration on a handful of occasions. Based on the 185 day periodicity, we predict a possible peak around 2007 Oct 20-30, which is consistent with our reported brightening being the start of a new major outburst.
We will observe the source again 2007 Oct 05 as part of the INTEGRAL Galactic Bulge monitoring program.
Follow-up observations are encouraged.